Paint, primer, sealants and other coatings usually undergo a chemical cure after being applied on a substrate, such as metal or plastic. The time allowed for curing these materials varies from a few minutes to many hours, and it is usually important to allow the cure to proceed to near completion before subsequent processes are performed. In the case of many coatings, it is important to apply a next coating before a previous coating is completely cured in order to assure good bonding between coating layers. In other cases, it is important for a coating to be completely cured before placement into service of a coated item, such as a fuel tank or a water tank.
However, determining state of cure or amount of cure may be difficult. Current coating cure tests include physical tests, such as a “dry-to-tape” test for primers and top coat paints and a tack-feel test for other coatings. These tests can be quite subjective and often may not give desired results.
Surface cleanliness has become more important because paint and primer systems have included more solids and less solvent over the past 10 years due to environmental regulations. High solids paint systems are more sensitive to surface contamination than are high solvent paint systems. Further, high solids paint systems may fail to adhere to a surface when a fairly low level contamination is present on the surface. For example, sufficient adherence of paint or primer to dielectric materials such as plastic and non-metallic surfaces depends upon cleanliness of the surface.
Known surface contamination measurement methods now available include portable fourier transform infrared (FT-IR) spectrometers, but these systems are heavy, bulky, and often cannot reach into a confined space. Surface contamination measurements with FT-IR systems require expert interpretation and detailed knowledge of system software and hardware.
Therefore, there exists an unmet need in the art for a simple and reliable method of measuring chemical cure and surface contamination.